Backcross
A cross between an animal that is heterozygous for alleles
obtained from two parental strains and a second animal from
one of those parental strains. Also used to describe the breeding
protocol of an outcross followed by a backcross.

Bacterial artificial chromosome (BAC)
Large segments of DNA, 100,000 to 200,000 bases, from another
species cloned into bacteria. Once the foreign DNA has been
cloned into the host bacteria, many copies of it can be made.
(NHGRI)

Bacteriophage
Structures are usually closed by main-chain hydrogen bonds
between the first and last strands of the beta sheet, in this
case it is defined by the two integer numbers: the number
of strand in the beta sheet, n, and a measure of the extent
the extent to which the strands in the sheet are staggered
the shear number, S. (SCOP)

Base
One of the molecules that form DNA and RNA molecules.

Base pair (bp)/b>
Two nitrogenous bases (adenine and thymine or guanine and
cytosine) held together by weak bonds. Two strands of DNA
are held together in the shape of a double helix by the bonds
between base pairs. (ORNL)

Base sequence
The order of nucleotide bases in a DNA molecule; determines
structure of proteins encoded by that DNA. (ORNL)

Behavioral genetics
The study of genes that may influence behavior. (ORNL)

Beta-sheet
Can be antiparallel (i.e. the strand direction in any two
adjacent strands are antiparallel), parallel (all strands
are parallel each other) and mixed (there is one strand at
least that is parallel to one of its two neighbours and antiparallel
to the other). (SCOP)

Bioinformatics
The merger of biotechnology and information technology with
the goal of revealing new insights and principles in biology.
(NCBI)

Bioinformatics
The science of managing and analyzing biological data using
advanced computing techniques. Especially important in analyzing
genomic research data.

Bioremediation
The use of biological organisms such as plants or microbes
to aid in removing hazardous substances from an area. (ORNL)

Biotechnology
A set of biological techniques developed through basic research
and now applied to research and product development. In particular,
biotechnology refers to the use by industry of recombinant
DNA, cell fusion, and new bioprocessing techniques. (ORNL)

Birth defect
Any harmful trait, physical or biochemical, present at birth,
whether a result of a genetic mutation or some other nongenetic
factor.

Bit score
The value S' is derived from the raw alignment score S in
which the statistical properties of the scoring system used
have been taken into account. Because bit scores have been
normalized with respect to the scoring system, they can be
used to compare alignment scores from different searches.
(NCBI)

Bits scores
Alignment scores are reported by HMMer and BLAST as bits scores.
The likelihood that the query sequence is a bona fide homologue
of the database sequence is compared to the likelihood that
the sequence was instead generated by a "random"
model. Taking the logarithm (to base 2) of this likelihood
ratio gives the bits score. (SMART)

BLAST
Basic Local Alignment Search Tool. (Altschul et al.) A sequence
comparison algorithm optimized for speed used to search sequence
databases for optimal local alignments to a query. The initial
search is done for a word of length "W" that scores
at least "T" when compared to the query using a
substitution matrix. Word hits are then extended in either
direction in an attempt to generate an alignment with a score
exceeding the threshold of "S". The "T"
parameter dictates the speed and sensitivity of the search.
For additional details, see one of the BLAST tutorials (Query
or BLAST) or the narrative guide to BLAST. (NCBI)

BLAST
A computer program that identifies homologous (similar) genes
in different organisms, such as human, fruit fly, or nematode.
(ORNL)

BLOSUM
Blocks Substitution Matrix. A substitution matrix in which
scores for each position are derived from observations of
the frequencies of substitutions in blocks of local alignments
in related proteins. Each matrix is tailored to a particular
evolutionary distance. In the BLOSUM62 matrix, for example,
the alignment from which scores were derived was created using
sequences sharing no more than 62% identity. Sequences more
identical than 62% are represented by a single sequence in
the alignment so as to avoid over-weighting closely related
family members. (Henikoff and Henikoff) (NCBI)

Bundle
An array of alpha-helices each oriented roughly along the
same (bundle) axis. It may have twist, left-handed if each
helix makes a positive angle to the bundle axis, or, right-handed
if each helix makes a negative angle to the bundle axis. (SCOP)